1. Field of the Invention
The present invention relates to a prismatic sealed battery module, and particularly relates to a prismatic sealed battery module which is formed by connecting a plurality of cells, and has a decreased internal resistance.
2. Description of Related Art
A conventional rechargeable battery module can provide a required electric power capacity by connecting a plurality of cells. This battery module is constituted such that a plurality of prismatic cells are placed while longer side surfaces of their cell case are opposingly brought into contact with each other, end plates are provided outside of the cell cases on both the ends, and the cells are integrally connected by binding with a tie band. Leads are pulled out upward from the top ends of electrode plates in the individual cells. The leads are connected with terminals provided on a cover of the cell case, and then the terminals between the cells are connected with each other through connection plates.
As a result, since connection paths between the cells are long, and the number of connection points is large, resistance caused by constitution parts including connection parts becomes high. A ratio of this part resistance to a reaction resistance caused by a battery reaction among a positive electrode plate, a negative electrode plate, and electrolyte reaches 40:60 to 50:50. Since this large internal resistance increases heat generation, increasing the output and enhancing life characteristics are seriously obstructed. Since the connection constitution between the cells is complicated, and the number of the parts is large, the cost also increases.
In light of the foregoing, the present applicant proposed a prismatic sealed battery module 100 including a plurality of cells 102 as shown in FIG. 10 and FIG. 11. The reference numeral 103 denotes a prismatic battery case which is formed as a flat rectangular solid. This battery case is constituted by integrally connecting a plurality of cell cases 104 used for the cells 102 formed as a prismatic shape including short side surfaces and long side surfaces while the short side surface is mutually shared as a partition wall 105. Openings on the top surface of the cell cases 104 are closed by a single cover 106. Connection holes 107 are formed on an upper part of the outside short side surfaces of the cell cases 104 on both the ends, and on an upper part of the partition walls 105 between the cell cases 104. The individual cell cases 104 store an electrode plate group 108 and electrolyte. The electrode plate group 108 is constituted by laminating a rectangular positive electrode plate and a rectangular negative electrode plate with a separator interposed between them. Consequently, the cell 102 is formed. The positive electrode plate and the negative electrode plate of the electrode plate group 108 protrude from the sides opposite to each other to form leads 109a and 109b for the positive electrode plate and the negative electrode plate. Collectors 110a and 10b are respectively connected with the side edges of the leads 109a and 109b by welding.
A connection protrusion 111 to be fit into the connection hole 107 is protrudingly formed at an upper part of the collectors 110a and 110b. The connection protrusions 111 of the positive and negative collectors 110a and 110b are connected with each other by welding between the neighboring cell cases 104. Positive and negative connection terminals 112 are also installed into the connection holes 107 on the outer short side surface of the cell cases 104 on both the ends. Then, a connection protrusion 113 of the connection terminal 112 and the connection protrusion 111 of the collector 110a or 110b are connected with each other by welding. Consequently, the plurality of cells 102 stored in the prismatic battery case 103 are connected serially, and a power is provided between the connection terminals 112 on both the ends.
With the constitution shown in FIG. 10 and FIG. 11, the current-carrying paths from the positive electrode plate and the negative electrode plate to the respective leads 109a and 109b, and the respective collectors 110a and 110b are short. However, since tips of the connection protrusions 111 on the top end of the collectors 110a and 110b are connected with each other at the one point by welding, the connection path is detoured, thereby increasing the length of the connection paths, and simultaneously the connection point is one as arrows in FIG. 12 show. Consequently, the internal resistance increases.